Lenses are commonly made by shaping an optical material such as glass. The weight of such lenses increases strongly with diameter making them very expensive and prohibitively heavy for applications requiring large area. Also the quality of a lens typically decreases with increasing size. Diffractive lenses such as Fresnel lenses are relatively thin, however, the structural discontinuity adds to aberrations. Uses of holographic lenses are limited by the compromise of efficiency and dispersion.
In the present invention, such components are obtained on the basis of diffractive waveplates. An exemplary structure of one of the optical components of interest is schematically shown in FIG. 1. Essentially, it is an optically anisotropic film 100 with the optical axis orientation 101 rotating in the plane of the film, the x,y plane in FIG. 1. The thickness L of the film is defined by half-wave phase retardation condition L=λ/(n∥−n⊥), where n∥ and n⊥ are the principal values of the refractive indices of the material; and λ is the radiation wavelength. The required half-wave phase retaradation condition can be met for as low as a few micrometer thick films, particularly, for liquid crystalline materials. Such a structure imposes a phase shift Φ=±2 α(x,y) on circular polarized beams propagating through it with the sign depending on the handedness of polarization. In simplest realization, the rotation angle α of the optical axis orientation is a linear function of a single coordinate, α=2πx/Λ with Λ characterizing the period of the pattern. With account of α=2πx/Λ=qx, where q=2π/Λ, an unpolarized beam is thus diffracted by the diffractive waveplate into +/−1st diffraction orders with the magnitude of the diffraction angle equal to λ/Λ. The phase Φ in the equation above, known as geometrical or Pancharatnam phase, does not depend on wavelength, hence the broadband nature of the diffraction. Due to its half-wave plate nature, there are well developed techniques for making the component essentially achromatic in a wide range of wavelengths. In case of quadratic variation pattern of the optical axis orientation, α˜x2 or, in two dimensional case, α˜x2+y2, the parabolic phase modulation profile produces cylindrical or spherical lens action, correspondingly.
Thus, there is a need and an opportunity provided by the current invention for fabricating lenses and other nonlinear phase modulating components that could be obtained in the form of thin film structurally continuous coatings on a variety of substrates.